Cooled blade for a gas turbine

ABSTRACT

In a cooled blade for a gas turbine, in which blade a cooling fluid, preferably cooling air, flows for convective cooling through internal cooling passages ( 141 - 143 ) located close to the wall and is subsequently deflected for external film cooling through film-cooling holes ( 161 - 163 ) onto the blade surface, and the fluid flow is directed in at least some of the internal cooling passages ( 141 - 143 ) in counterflow to the hot-gas flow ( 18 ) flowing around the blade, homogeneous cooling in the radial direction is achieved owing to the fact that a plurality of internal cooling passages ( 141 - 143 ) and film-cooling holes ( 161 - 163 ) are arranged one above the other in the radial direction in the blade ( 10, 20, 30 ) in such a way that the discharge openings of the film-cooling holes ( 161 - 163 ) in each case lie so as to be offset from the internal cooling passages ( 141 - 143 ), in particular lie between the internal cooling passages ( 141 - 143 ).

[0001] The present invention relates to the field of gas-turbinetechnology. It concerns a cooled blade for a gas turbine according tothe preamble of claim 1.

[0002] Such a blade has been disclosed, for example, by the publicationWO 99/06672.

[0003] To increase the output and the efficiency, ever increasingturbine inlet temperatures are used in modern gas-turbine plants. Inorder to protect the turbine blades from the increased hot-gastemperatures, these blades have to be cooled more intensively thanhitherto. At correspondingly high turbine inlet temperatures, bothconvective cooling and film-cooling elements are used. In order toincrease the effectiveness of these types of cooling, it is desirable toreduce the wall-material thicknesses. Furthermore, optimum distributionbetween convective heat absorption of the cooling fluid andcooling-fluid temperature during the blow-out as cooling film is to beaimed at.

[0004] Combinations of convective cooling and film cooling at reducedwall thicknesses have been disclosed, for example, by U.S. Pat. Nos.5,562,409, 4,770,608 mentioned at the beginning, and U.S. Pat. No.5,720,431. In this case, the convective cooling is carried out viaimpingement cooling, only a small part of the surface being cooled bythe respective cooling-fluid jet, which is subsequently used for thefilm cooling. The convective cooling capacity of the fluid is thereforeonly partly utilized.

[0005] U.S. Pat. Nos. 5,370,499 and 5,419,039 describe a method ofavoiding this disadvantage. In this case, the cooling fluid is first ofall used for convective cooling in passages close to the wall before itis blown out as a film. At the same time, the convective coolingpassages may be provided with turbulence-increasing devices (ribs,cylinders or crossed passages). However, the cooling fluid is alwaysdirected in these devices in parallel with the main-gas flow, which doesnot constitute the best solution for optimum cooling.

[0006] In the publication WO-A1-99/06672 mentioned at the beginning, ithas now been proposed to direct the cooling fluid in the convective partin an antiparallel manner, i.e. in counterflow to the main-gas flow (andthus to the film-cooling flow). This certainly results in cooling whichis more homogeneous in the axial direction or in the direction of thehot-gas flow. However, it is still open to question as to howhomogeneous cooling or temperature distribution in the longitudinaldirection of the blade, that is in radial extent, can be achieved.

[0007] The object of the invention, then, is to provide a cooledgas-turbine blade which also ensures a homogeneous distribution of thematerial temperature at the blade in the radial direction.

[0008] The object is achieved by all the features of claim 1 together.

[0009] The essence of the invention consists in arranging a plurality ofinternal cooling passages and film-cooling holes one above the other inthe radial direction in the blade in such a way that the dischargeopenings of the film-cooling holes in each case lie so as to be offsetfrom the internal cooling passages, and in particular lie between theinternal cooling passages. Since the cooling effect of the film coolingbetween the holes is less than in the axial direction downstream of theholes, the cooling effect of the internal cooling is utilized in theseintermediate regions by the arrangement according to the invention.

[0010] The cooling fluid is first of all directed in counterflow to thehot-gas flow in convective passages close to the wall, which areintegrated in the overall structure and can be provided withturbulence-generating devices, before the cooling fluid is used for filmcooling. As a result, very uniform temperature distributions areproduced, which is very important for the small wall thicknesses desiredand the low wall thermal resistance associated therewith, since thetemperature balance is impaired by heat conduction in the wall at smallwall thicknesses. Furthermore, due to the deflection of the coolingfluid, which automatically occurs, an impulse can be applied, and thisimpulse is advantageous for the cooling effect of the cooling film, ashas been described, for example, in U.S. Pat. No. 4,384,823, or a swirlcan also be produced in the “prechamber” of the film-cooling hole, asdescribed in U.S. Pat. No. 4,669,957.

[0011] A first preferred embodiment of the blade according to theinvention is distinguished by the fact that turbulence-generatingelements are arranged in the internal cooling passages. In this way, thecontact between cooling fluid and passage wall and thus the internalcooling can be further improved.

[0012] Specific setting of the cooling can be achieved if, in a secondpreferred embodiment of the invention, cavities are arranged in theinternal cooling passages for setting the cooling-fluid pressure or thecooling-fluid mass flow.

[0013] The internal cooling can also be improved if, in anotherpreferred embodiment, first ribs are arranged in the internal coolingpassages for enlarging the heat-transfer area, in which case, inparticular, the first ribs are designed so as to alternate in the flowdirection as outer ribs and inner ribs, and in the inner ribs have alarger height and/or width than the outer ribs.

[0014] A further increase in the cooling effect in the interior isachieved if, in a further preferred embodiment of the invention, firstimpingement-cooling holes are provided in order to supply the internalcooling passages, through which impingement-cooling holes the coolingfluid enters the internal cooling passages in the form of impingementjets.

[0015] In addition to the internal cooling passages, a cooling passagemay also be arranged in the blade nose, to which cooling passage coolingfluid is admitted through second impingement-cooling holes, in whichcase second film-cooling holes are preferably directed from the coolingpassage to the blade surface, the second impingement-cooling holes andthe second film-cooling holes are arranged alternately, and second ribsare arranged between the second impingement-cooling holes and the secondfilm-cooling holes for increasing the heat-transfer area and forseparating the zones of the cooling passage which belong to the secondimpingement-cooling holes and the second film-cooling holes.

[0016] The internal cooling passages may run axially, and thefilm-cooling holes may in each case branch off from an associatedinternal cooling passage at an angle in the radial direction. However,it is also conceivable for the internal cooling passages to run axially,for the ends of the internal cooling passages to be connected by radialpassages, and for the film-cooling holes to in each case be arrangedbetween the internal cooling passages and start from the radialpassages. Furthermore, it is conceivable in this connection for theinternal cooling passages to run at an angle in the radial direction,and for the film-cooling holes to in each case branch off from anassociated internal cooling passage in the axial direction, or for theinternal cooling passages to run at a first angle in the radialdirection, and for the film-cooling holes to in each case branch offfrom an associated internal cooling passage at a second angle in theradial direction. In all cases, the film-discharge surfaces are arrangedso as to be offset from the convective internal cooling passages, sothat the internal cooling takes place precisely where the film coolingis less effective.

[0017] Further embodiments follow from the dependent claims.

[0018] The invention is to be explained in more detail below withreference to exemplary embodiments in connection with the drawing, inwhich:

[0019]FIG. 1 shows, in a cross section of the marginal region, a firstpreferred exemplary embodiment for an individual internal coolingpassage with cooling fluid directed in counterflow to the hot-gas flow,without and with additional turbulence-generating means, in a bladeaccording to the invention;

[0020]FIG. 2 shows an exemplary embodiment comparable with FIG. 1 havingcavities in the internal cooling passages for setting the cooling-fluidmass flow;

[0021]FIG. 3 shows an exemplary embodiment comparable with FIG. 1 havingadditional ribs in the internal cooling passage for enlarging theheat-transfer area;

[0022]FIG. 4 shows, in a cross section, the leading-edge region of acooled blade in another exemplary embodiment of the invention having anadditional cooling passage in the blade nose;

[0023]FIG. 5 shows, in an enlarged detail from FIG. 4, the blade nosewith additional subdividing ribs in the cooling passage close to theedge;

[0024] FIGS. 6-9 show various exemplary embodiments for the (offset)arrangement according to the invention of internal cooling passages andfilm-cooling holes in the radial direction of the blade in a bladeaccording to the invention;

[0025]FIG. 10 shows two preferred exemplary embodiments for thearrangement of a plurality of film-cooling holes for each internalcooling passage in a blade according to the invention;

[0026]FIG. 11 shows an exemplary embodiment of the blade according tothe invention having a deflection of the fluid flow into the counterflowby specific directing of the internal cooling passages; and

[0027]FIG. 12 shows another exemplary embodiment of the blade accordingto the invention having a deflection of the fluid flow by thepositioning of the feeds (impingement-cooling holes) for the coolingfluid to the internal cooling passages.

[0028] For a blade according to the invention, a first preferredexemplary embodiment of an individual internal cooling passage havingcooling fluid directed in counterflow to the hot-gas flow, without andwith additional turbulence-generating means, is shown in FIG. 1 in across section of the marginal region. The blade 10 is exposed with itsblade surface 11 to a hot-gas flow 18 (long arrow pointing from right toleft). Arranged below the blade surface 11 are internal cooling passages14, which are separated from the blade surface 11 only by a thin wall 12of thickness D and run parallel to the blade surface 11. A coolingfluid— preferably cooling air—is fed at one end to the internal coolingpassages 14, preferably via impingement-cooling holes 13. The coolingfluid then passes through the internal cooling passages 14 incounterflow to the (external) hot-gas flow 18. It is deflected in adeflection space 15 located at the other end of the internal coolingpassages 14 and leaves the blade 10 as a film flow 17 throughfilm-cooling holes 16, which start from the deflection space 15 in thedirection of the hot-gas flow 18, in order to form a cooling film on theblade surface 11. In this case, the internal cooling passages 14 mayhave smooth walls, but may also be provided with turbulence-generatingelements 19, 19′ known per se, as can be seen on the right in FIG. 1.

[0029] This type of cooling is based on the idea of directing thecooling fluid first of all in counterflow to the hot-gas flow 18 inconvective passages located close to the wall, which are integrated inthe overall structure and can be provided with turbulence-generatingdevices, before the cooling fluid is used for the film cooling. As aresult, very uniform temperature distributions are produced, which isvery important for the small wall thicknesses D desired and the low wallthermal resistance associated therewith, since the temperature balanceis impaired by heat conduction in the wall 12 at small wall thicknesses.Furthermore, due to the deflection of the cooling fluid, whichautomatically occurs, an impulse can be applied, and this impulse, asalready mentioned at the beginning, is advantageous for the coolingeffect of the cooling film forming on the surface.

[0030] Furthermore, according to FIG. 2, the convectively cooledinternal cooling passages 14 may be provided with larger cavities 21which enable the fluid pressure to be set in order to improve thefilm-cooling effectiveness and set the desired cooling-fluid mass flow.

[0031]FIG. 3 shows a further variant, by means of which the fluidpressure can be set and the surface necessary for the heat dissipationcan be enlarged and the turbulence and thus the heat transfer can beincreased. In this case, the integral convective internal coolingpassages 14 are directed serpentine-like around inner and outer ribs 23and 22 respectively. The internal cooling passage is again fed withcooling fluid by one (or more) impingement-cooling hole(s) 13. Thecooling fluid is then passed as a cooling film (through film-coolingholes 16 which are angled in the flow direction and/or in the lateraldirection and may be provided with diffuser extensions) in counterflowonto the outer blade surface 11. On account of the different temperatureconditions, the inner ribs 23 should preferably be designed to be largerin height and/or width than the outer ribs 22.

[0032] Especially effective cooling can be achieved with this coolinggeometry according to FIG. 4 in the leading-edge region of a gas-turbineblade, in which case a combination with an impingement-cooled (andpossibly film-cooled) blade nose 43, as described in Patent EP-A1-0 892151, is possible. Accommodated in this case in the walls of the blade 40are a plurality of the cooling arrangements 44-46 already described,which in each case comprise internal bores 14, which are supplied withcooling fluid in counterflow on the inlet side from a (radial) mainpassage 50 via impingement-cooling holes 13 and allow the cooling fluidto discharge as a cooling film on the outlet side via deflection spaces15 and film-cooling holes 16 onto the blade surface (pressure surface 41or suction surface 42). Provided for cooling in the blade nose 43 is acooling passage 47, which is supplied from the main passage 50 throughimpingement-cooling holes 49 and delivers the cooling film to theoutside via film-cooling holes 48.

[0033] At the same time, the configuration specified, according to FIG.5, may be advantageously extended with the outer ribs 51 describedabove. These ribs 51, which may also be interrupted in the radialdirection and then constitute rib segments (or pins), increase theheat-dissipating surface and separate those surfaces which are struck bythe impingement jets from the impingement-cooling holes 49 from thecavities from which the film-cooling holes 48 start. In this case, thefilm-cooling holes 48 may be arranged at an angle in the radialdirection (perpendicular to the drawing plane of FIG. 5). This achievesthe effect that the cooling fluid sweeps over the entireheat-dissipating surface available and high cooling effectiveness isachieved.

[0034] The arrangements specified permit a homogeneous materialtemperature distribution in the flow direction of the hot-gas flow 18,i.e. in the axial direction of the gas turbine. However, it is essentialfor the invention to also achieve a homogeneous distribution in radialextent (perpendicular to the drawing plane in FIGS. 1 to 5) in order toincrease the service life of a gas-turbine blade. This is ensured by thespecial arrangement according to the invention of internal coolingpassages and film-cooling holes. It is essential in this case to havearrangements in which the film-discharge surfaces (discharge openings ofthe film-cooling holes) are arranged so as to be offset from theconvective internal cooling passages. Since the cooling effect of thefilm cooling between the holes is less than in the axial directiondownstream of the holes, the cooling effect of the internal cooling canbe utilized in these intermediate regions.

[0035] FIGS. 6-9 show possible basic arrangements which follow thisidea. In FIG. 6, a plurality of internal cooling bores 141-143 arearranged in the radial direction 52 of the blade one above the other andso as to run parallel to one another at a uniform distance apart in theaxial direction (parallel to the hot-gas flow 18). Film-cooling holes161-163 go from the outlet-side ends of the internal-cooling passages141-143 to the blade surface, which lies in the drawing plane. Thefilm-cooling holes 161-163 are made at an angle in the radial direction,so that their (oval) film-discharge openings are in each case arrangedbetween the internal cooling passages 141-143 lying in the wall.

[0036] Shown in FIG. 7 is an arrangement in which the ends of internalcooling passages 141-143 running axially in the wall are connected byradial passages 24. The film-cooling holes 161-163 are made between theinternal cooling passages 141-143 so as to start from the radialpassages 24 and run parallel to the internal cooling passages 141-143.

[0037]FIG. 8 shows a further possibility. The internal cooling passages141-143 are in this case made in the blade wall at an angle in theradial direction, whereas the film-cooling holes 161-163 branching offfrom them run axially. Combinations of these arrangements areconceivable, as shown in FIG. 9 for example. In this case, both theinternal cooling passages 141-143 and the film-cooling holes 161-163 aremade at an associated angle in the radial direction. The matrixstructure produced is especially effective for homogenization of thematerial temperature in the radial direction. In all cases, a pluralityof film-cooling holes 161-161″ and 162-162″ for each internal coolingpassage 141 and 142 respectively are also conceivable, as shown in FIG.10 for angled passages and axial holes (part A of figure; comparablewith FIG. 8) and respectively for angled passages and angled holes (partB of figure; comparable with FIG. 9). This is of course also possiblefor the other arrangements described.

[0038] The counterflow principle according to the invention for thehomogenization of the wall temperature in the axial and radialdirections may also be realized by the convective internal coolingpassages 141-143 themselves, as indicated in FIGS. 11 and 12. In thiscase, for the internal cooling air, the counterflow is achieved eitherby deflections 53, 54 (FIG. 11) or by feeding and discharging thecooling medium (e.g. via impingement-cooling holes and the film-coolingholes, as described above) at different axial positions (FIG. 12).

List of Designations

[0039]10, 20, 30 Blade (gas turbine)

[0040]11 Blade surface

[0041]12 Wall

[0042]13 Impingement-cooling hole

[0043]14 Internal cooling passage

[0044]15 Deflection space

[0045]16 Film-cooling hole

[0046]17 Film flow

[0047]18 Hot-gas flow

[0048]19, 19′ Turbulence-generating element

[0049]21 Cavity

[0050]22, 23 Rib

[0051]24 Radial passage

[0052]40 Blade (gas turbine)

[0053]41 Pressure surface

[0054]42 Suction surface

[0055]43 Blade nose

[0056]44-46 Cooling arrangement

[0057]47 Cooling passage

[0058]48 Film-cooling hole

[0059]49 Impingement-cooling hole

[0060]50 Main passage

[0061]51 Rib or rib segment

[0062]52 Radial direction (blade)

[0063]53, 54 Deflection

[0064]141-143 Internal cooling passage

[0065]161-163 Film-cooling hole

[0066]161′, 161″ Film-cooling hole

[0067]162′, 162″ Film-cooling hole

[0068] D Thickness (wall)

1. A cooled blade (10, 20, 30, 40) for a gas turbine, in which blade(10, 20, 30, 40) a cooling fluid, preferably cooling air, flows forconvective cooling through internal cooling passages (14; 141-143)located close to the wall and is subsequently deflected for externalfilm cooling through first film-cooling holes (16; 161-163; 161′, 162″;162′, 162″) onto the blade surface (11), the fluid flow being directedin at least some of the internal cooling passages (14; 141-143) incounterflow to the hot-gas flow (18) flowing around the blade (10, 20,30, 40), characterized in that a plurality of internal cooling passages(141-143) and film-cooling holes (161-163) are arranged one above theother in the radial direction in the blade (10, 20, 30) in such a waythat the discharge openings of the film-cooling holes (161-163) in eachcase lie so as to be offset from the internal cooling passages(141-143), in particular lie between the internal cooling passages(141-143).
 2. The blade as claimed in claim 1 , characterized in thatturbulence-generating elements (19, 19′) are arranged in the internalcooling passages (14; 141-143).
 3. The blade as claimed in either ofclaims 1 and 2, characterized in that cavities (21) are arranged in theinternal cooling passages (14; 141-143) for setting the cooling-fluidpressure or the cooling-fluid mass flow.
 4. The blade as claimed in oneof claims 1 to 3 , characterized in that first ribs (22, 23) arearranged in the internal cooling passages (14; 141-143) for enlargingthe heat-transfer area.
 5. The blade as claimed in claim 4 ,characterized in that the first ribs (22, 23) are designed so as toalternate in the flow direction as outer ribs (22) and inner ribs (23),and in that the inner ribs (23) preferably have a larger height and/orwidth than the outer ribs (22).
 6. The blade as claimed in one of claims1 to 5 , characterized in that first impingement-cooling holes (13) areprovided in order to supply the internal cooling passages (14; 141-143),through which impingement-cooling holes (13) the cooling fluid entersthe internal cooling passages (14; 141-143) in the form of impingementjets.
 7. The blade as claimed in one of claims 1 to 6 , characterized inthat the cooling fluid is deflected in the direction of the hot-gas flow(18) before discharge from the first film-cooling holes (16; 161-163;161′, 161″; 162′, 162″).
 8. The blade as claimed in one of claims 1 to 7, characterized in that, in addition to the internal cooling passages(14; 141-143), a cooling passage (47) is arranged in the blade nose(43), to which cooling passage (47)cooling fluid is admitted throughsecond impingement-cooling holes (49).
 9. The blade as claimed in claim8 , characterized in that second film-cooling holes (48) are directedfrom the cooling passage (47) to the blade surface (11), in that thesecond impingement-cooling holes (49) and the second film-cooling holes(48) are arranged alternately, and in that second ribs or rib segments(51) are arranged between the second impingement-cooling holes (49) andthe second film-cooling holes (48) for increasing the heat-transfer areaand for separating the zones of the cooling passage (47) which belong tothe second impingement-cooling holes (49) and the second film-coolingholes (48).
 10. The blade as claimed in one of claims 1 to 9 ,characterized in that the internal cooling passages (141-143) runaxially, and the film-cooling holes (161-163) in each case branch offfrom an associated internal cooling passage (141-143) at an angle in theradial direction.
 11. The blade as claimed in one of claims 1 to 9 ,characterized in that the internal cooling passages (141-143) runaxially, in that the ends of the internal cooling passages (141-143) areconnected by radial passages (24), and in that the film-cooling holes(161-163) are in each case arranged between the internal coolingpassages (141-143) and start from the radial passages (24).
 12. Theblade as claimed in one of claims 1 to 9 , characterized in that theinternal cooling passages (141-143) run at an angle in the radialdirection, and the film-cooling holes (161-163) in each case branch offfrom an associated internal cooling passage (141-143) in the axialdirection.
 13. The blade as claimed in one of claims 1 to 9 ,characterized in that the internal cooling passages (141-143) run at afirst angle in the radial direction, and the film-cooling holes(161-163) in each case branch off from an associated internal coolingpassage (141-143) at a second angle in the radial direction.
 14. Theblade as claimed in one of claims 1 to 13 , characterized in that ineach case a plurality of film-cooling holes (161-161″; 162-162″) branchoff from an internal cooling passage (141, 142) in such a way as to bedistributed over the passage length.
 15. The blade as claimed in one ofclaims 1 to 14 , characterized in that deflections (53, 54) are providedin the internal cooling passages (141, 142) for producing thecounterflow.
 16. The blade as claimed in one of claims 1 to 14 ,characterized in that the cooling medium is fed to the internal coolingpassages (142-143) at different axial positions for producing thecounterflow.